1. Field of the Invention
The present invention relates to a process for improving hydrogen purity and the apparatus for effecting the same.
2. Related Art
A conventional hydrogen purity improving method is the batch system described in JP-A-3-27110 and 7-267607. According to such a system, while hydrogen is actively recovered from an impure gas source from a generator so that it may be reused, a remaining amount of impure gas is discharged to the atmosphere, whereby improvement in the hydrogen purity is conducted effectively.
The apparatus described in JP-A-3-271101 is characterized in that a hydrogen-utilizing generator and a hydrogen recovery container having a heating unit, a cooling unit and a hydrogen absorbing alloy therein, are connected with a pipe having a first pressure-controlling valve. In addition, the hydrogen recovery container employs a purging gas line having a second pressure-controlling valve activated with respect to a pressure corresponding to the internal pressure of the hydrogen recovery container. A product gas line having the first valve and a discharging gas line having the second valve are respectively connected with the hydrogen recovery container.
According to this hydrogen purity improving apparatus, hydrogen gas in the hydrogen-utilizing unit is sufficiently occluded in a hydrogen absorbing alloy in the hydrogen recovery container. Next, in releasing hydrogen gas from the hydrogen recovery container, hydrogen gas, including a substantial amount of impure gas from the hydrogen recovery container, is momentarily released from the releasing gas line. Thereafter, hydrogen gas having a high purity, released from the hydrogen absorbing alloy, is returned to the hydrogen-utilizing unit through the product gas line.
Since this apparatus is equipped with only one hydrogen recovery container, the construction of the apparatus is simple, which is resulted in a low cost, and the maintenance of the apparatus is reasonable. However, the technical problem of a low hydrogen recovery may arise. Namely, after introducing hydrogen gas in the hydrogen-utilizing unit into the hydrogen recovery container according to the batch manner, hydrogen gas including a substantial amount of impure gas from the hydrogen recovery container is released outside through the releasing gas line in the initial stage where hydrogen is released from the absorbing alloy. Thus, hydrogen included in the purged impure gas cannot be recovered.
On the other hand, the hydrogen purity improving apparatus described in JP-A-7-267607 is characterized by a hydrogen-utilizing generator connected in parallel with, plural hydrogen recovery containers. Each hydrogen recovery container employs a hydrogen absorbing alloy occluding hydrogen as a hydride, a cooling unit and a heating unit. A first valve and a second valve each having a switch function are provided at the hydrogen inlet side of each parallel hydrogen recovery container. In addition, a third valve and a fourth valve are provided at the hydrogen outlet side of each hydrogen recovery container, each having a switch function. A recycling pipe is connected in line with each hydrogen recovery container and equipped with valves arranged in series and having a switch function. Purging gas lines having a purging valve are connected with each hydrogen recovery container at the hydrogen outlet side thereof.
According to this conventional hydrogen purity improving apparatus, hydrogen can be recovered from the purged gas from one hydrogen recovery container and reused. Thus, hydrogen recovery is improved. However, hydrogen gas including a substantial amount of impure gas is introduced into another hydrogen recovery container in which the impure gas-containing hydrogen gas is occluded again in the hydrogen absorbing alloy. Therefore, plural hydrogen recovery containers having a complicated structure are required, which results in a high cost. Further, the maintenance of the apparatus is significant. Still further, since oxygen which is harmful to the hydrogen absorbing alloy comes into contact with the hydrogen absorbing alloy for a longer period of time, potential deterioration of the hydrogen absorbing alloy is increased within a short time even though a substantial amount of the hydrogen absorbing alloy is accommodated in the plural hydrogen recovery containers.